In many pump applications, such as in irrigation pumps, there is a trend toward the use of diesel engines to drive the pump shaft. In order to operate efficiently from a fuel conservation standpoint, a diesel engine should operate at a low RPM. This requires that the pump impeller have a large diameter. By way of example, in the case of irrigation pumps of the indicated type, the impeller diameter may be as large as seventeen inches. Heretofore, many irrigation pumps have used bronze impellers in order to prevent corrosion, especially in the close fitting clearance ring area. Fertilizers of various types are often mixed with the liquid being pumped and make the liquid corrosive, even to bronze. Obviously the use of corrosion resistant materials such as bronze or stainless steel would be prohibitive from a cost standpoint, especially when large diameter impellers are used. For economy, for resistance to wear and for withstanding the effects of certain chemicals, it would be desirable to make the impeller out of cast iron. However, the use of a cast iron impeller would not be satisfactory if one used the present-day means for providing a close clearance space between the rotating impeller and the volute body. A cast iron impeller would rust rapidly at this clearance location whereby the impeller would "bind" and the leakage from the discharge side of the impeller to the inlet side would become too great to maintain a satisfactory pump efficiency. A close fit must be maintained at this clearance location in order to maintain the efficiency and to achieve the low fuel consumption desired.
In accordance with the invention, such a clearance space design for a cast iron impeller has been provided. This means includes a corrosion resistant ring mounted in the volute body of the pump and extending around a portion of the impeller hub. A stainless steel tubular insert member is cast into this portion of the impeller hub so as to cooperate with the clearance ring to define the clearance space therebetween. The clearance ring and stainless steel insert member define cooperating surface portions between the rotating impeller and the volute body in the manner to resist corrosion and wear and to maintain a minimum clearance space. The clearance ring may be made in the form of a bendable or flexible ring adapted to be compressed from its normal condition when inserted into its mounted position within a bore in the pump body so as to spring outwardly into its fitted position.
By reason of the novel construction of the invention, the impeller may be made from a relatively inexpensive material such as cast iron. At the same time, the clearance space between the impeller and the volute body is formed by a pair of cooperating members which can withstand wear and are highly corrosion resistant. The use of the bendable corrosion ring provides the advantage that the clearance ring can be replaced easily in the event of wear thereof.